Conventional telephone network monitoring systems are typically intrusive and therefore channels to be monitored are normally put out of service while monitoring is taking place.
Various types of signaling are employed to transmit telephone data, including MFC R2D signalling, CCITT #5 signalling and CCITT #7 signalling.
MFC R2D signalling (also termed herein "R2D") is specified in CCITT Rec. Q. 400 to Q. 490. R2D is a CAS (channel associated signalling) system. Signalling information is transmitted over the same 2.038 Mbit/s trunk as is carrying the voice traffic. Information about telephone digits, also termed address signalling, is transmitted using inband MF tones in the forward and backward directions, information about call setup conditions, also termed line signalling, is transmitted by using the A and B units of time-slot 16 of an E1 carrier.
CCITT #5 signalling (also termed herein "C5" and "SS5") is specified in CCITT Rec. Q.140 to Q.164. As for the R2D, signalling information is transmitted over the same trunk as is carrying the voice traffic. 2400 Hz and 2600 Hz inband signalling tones are used to represent various call setup conditions. Tone durations of 40 ms and 125 msec are used.
CCITT #7 signalling (also termed herein "C7" and "SS7") is specified in CCITT Rec. Q.700 to Q.795 (volume VI.7-9, Blue Book). SS7 is a common channeling signalling system (CCS), in which signalling information is transmitted in dedicated n.times.64 kbit/s signalling channels, using data communications protocols. The traffic and the corresponding signalling information for a call are most often transmitted over different E1 carriers. In the present specification and claims, the term "CCITT #7" is intended to include ANSI SS7 signalling.